I don’t think orbital access will soon become so cheap that participants will be content to stay inside, and not be allowed to “go outside and play”: flights to Hawaii are not cheap enough for that. Some of us still remember White’s “sigh”;

Finally, after 15 minutes 40 seconds, McDivitt broke off to ask the ground if they wanted anything. "Yes," Kraft chuckled, "Tell him to get back in." And when McDivitt had to tell White it was time to come back inside, Mission Control and the whole world heard him sigh, "It's the saddest moment of my life."

It would be a good time to start removing misconceptions about Spacewalks (EVA). There is no reason for them to be more dangerous than SCUBA diving, which millions participate in safely. I know you can’t breathe vacuum, but you can’t breathe water either. Many people prove that each year (by drowning), but that doesn’t stop the rest of us from having fun!

First, it is easy to be carried out to sea by currents, but very difficult to “drift away” from a space station. Normally, if you TRY to get away, your intersecting orbit brings you right back to the station in 90 minutes or less. You are of course never out of sight, or out of radio range – both exceed a thousand miles, and you are unlikely to be on a course that loops more than a mile or two away before swinging back. Air isn’t a problem, for a small Oxygen tank can supply you for twenty hours, and your CO2 scrubbers can easily be designed to handle twelve.

While this is far safer than SCUBA diving, it would be wise to use the “buddy system”, at least to keep you from FEELING lost, and panicking. It doesn’t take much to make your pressure suit and breather “fail safe”, so that even a severe cut or rip will cause no lasting damage. Umbilical systems and tethers are a much bigger problem and can be very dangerous in a frictionless environment.

You will of course want maneuvering thrusters. And most of you will want an automatic stabilization system. The latter can use “camcorder” stabilization circuits. When activated, this will correct a confusing tumble, and bring you to rest. The thrusters can actually be as simple as a “Dust Off” can. Even that will keep you from floundering helplessly, and let you drift slowly back to the station. You will probably be wearing redundant sets of thrusters, as well as playing with a simple hand device. And if you get too tired or confused to deal with these systems, the lifeguard will puff in your direction, and take you in tow (or just activate your systems by radio control). GPS works extremely well in orbit, and will locate you to a millimeter so the lifeguard will know exactly how to bring you smoothly home, while you listen to his reassuring words.

If this picture of awesome beauty, dreamlike flight and perfect safety are hard to believe, blame it on bad press. Many professional sailors hate water and don’t know how to swim. NASA has never had the time or motivation to develop “easy EVA”. But “Space Tourists” will demand it, so we should start designing the equipment!

I have thought in the past that a lot of equipment currently used in our oceans could be adapted for use in space.

For instance I did not understand why a new robot arm had to be developed for the shuttle so that it could inspect the heat shield, why not use an underwater remote control camera system and replace its propellers with small cold gas thrusters. A small light weight camera sytem for use in space would probably have been much easier to build, cheaper and have a much further range. Such a camera would have been able to operate all over the ISS and not be limited to near the shuttle.

_________________A journey of a thousand miles begins with a single step.

Your suggestion of a remote Shuttle Inspection Unit (SIU) stimulated me to review the maneuvering components which would work in this very small package.

(This might also be a better initial demonstration in a "Zero G" aircraft flight. For this use it might be necessary to substitute small fans for the thrusters, because of FAA safety concerns. On the other hand, CO2 powered jets could use the same cartridges embedded in each of the under seat Life Jackets, so this objection may be surmountable.)

The smallest stock electromechanical valves I know off are the "ink jet" valves from www.theleeco.com. These actually weight 6 grams each. Full attitude and positional maneuvering (6 "degree of freedom") requires 12 valves. These work in torque balanced pairs to produce the 3 linear accelerations, and in thrust balanced pairs to create the 3 angular accelerations. Each thrust jet is mounted back to back with an opposing twin to create reversed forces when needed. The 72 gram mass for this collection is pretty small, even when the rest of the necessary parts are added. The flow through these valves is so small that use with a liquid like Freon would be necessary. It would then be necessary to electrically heat a small "expansion chamber" on the back of each jet to get proper evaporation - "flash boiling" liquids give a considerably reduced "specific impulse".

For human maneuvering I prefer CO2 (stored as a liquid) as a fuel. I am actually using "Paintball" tanks and parts. Two or three "20 ounce" tanks looks good, with the last one as a spare, since pressure gives a poor indication of remaining fuel with CO2. On the other hand, the CO2 system does a good job of cooling a pressure suit, and the heat captured in that mode adds to the energy available for thrust - a nice synergy.

Note that increasing the thruster group from 12 to 16 (with a tetrahedral array, instead of the Cartesian array) gives complete redundancy for failed thrusters.

For very small systems, attitude control becomes very tricky using the jets, and zero motion can seldom be accomplished. This is less of a problem for linear motion, because a camera slowly "trucking" (somewhat like panning) across the field of interest can provide superb stereoscopic images! These provide much more accurate understanding of a object than flat pictures. With telephoto lenses, "hyper stereo" can accurately mimic close up inspection, even stereo microscope inspection, with the camera 10 to 100 feet away for safety and convenience.

I would elect to use rotating inertia wheels for this system (with a nutation damper). They don't replace the attitude jets, because they have a limited ability to "absorb" applied torques. But they allow precision adjustments and consume no fuel while maintaining dead accurate alignment. I would also use the larger, 30 gram solenoid valves, most of them controlling gas rather than liquid flow. The three MEMS (Micro Electro Mechanical System) rate gyros needed weigh under one gram each. Stock, infrared horizon and sun sensors are actually heavier, but would total under 20 grams. A one gram, three axis magnetic sensor would complete the set, providing redundant systems for automatic alignment.

A GPS system, operating in "carrier phase detection", differential mode could reduce locational errors relative to the shuttle to millimeters. This system would probably total 2 to 3 kilograms, with multiple, high resolution color (and infrared) cameras. Built with rather common, commercial hardware, this unit would have a price low enough to be disposable. With a few hundred grams of Freon, total maneuvering "Delta V" would be 30 to 100 meters per second, but there is no need to be in a hurry. Even one meter per second (with an equal and opposite burst to stop) would position the SIU ONE KILOMETER distant, at the 1000 sec time point which roughly ends the "linear time phase". During this time, in LEO, orbital dynamics produces only modest "windage" type corrections to classical mechanics. As the time grows to multiples of this interval, maneuvering efforts usually backfire - as often pointed our in popular literature.

A human attempting rendezvous with manual control is not working with the later effects, because he will always be too impatient to wait more than 1000 seconds to see the result of his actions! An inexperienced human, without automated aids, is simply not prepared for the lack of friction, and will repeatedly overshoot both in angular orientation and in position. Video games which accurately simulated this were not very popular (and may have completely disappeared).

I really look forward to the gymnastic masterpieces that athletes skilled in free spaceflight will create in sport, and dance!